The thing that really gives GT2 it's name is it's variety. There are no cars with 3 different names like in GT5. RMs where also nice too, since they're VERY cheap to get very early on.
Everybody here who knows me won't be surprised to hear GT2 is my favorite. 12 years later and I'm still not close to being done having fun with it, so much so that I've not yet played GT3, GT4, or GT5...
But I'm replying mainly to list the multiples in GT2, of which there are in fact a few. And other than the obvious multiples, there are the many variations of essentially the same model, with sometimes inexplicably better performance coming from the older models! But this is part of the charm of GT2 for me.
Camaro Z/28 Coupe '97 and 30th Anniversary edition, same cars really
Mustang GT '98 and '99, too close to tell the diff, also with SVT Cobras
Accord SiR-T '97 and '98
Beat normal, Ver F and Ver Z
5 NSX GT's
Esprit V8 GT and SE
all the cars with Aero versions are the same except slight cosmetic diff
2 GT-R R33 GT's
3 GT-R R34 GT's
Stagea Autech Ver 260RS '97 and '98
3 Celica SS-II's are basically the same, though Elegant gets less peak hp
GT-One Race Car '98 and '99
Levin/Trueno duplicates except pop-up lamps, and '83 and '85 are basically the same, so that's 4 of the same in that generation, and then 2 each in '96 and '98
3 Supra GT's
2 Silvia GT's
... okay, that's not so bad, still like 575 out of 600 unique